Wow! What a great buy, well done.

I think you'd need a fair bit of dye to do curtains and I don't think it would really work well. The more natural fibres something has the better it dyes, so I don't think curtains are a candidate.

I do like the idea of lace curtains over the top. Or maybe a sheer curtain rather than lace (can be a bit dated). Spotlight often has lace curtaining on special and it is pretty cheap too. But I don't think it would look fantastic...

Another idea would be to move your lounge suite around the in room away from the curtains? Or get some cushions and throws to "break up" the colour. Maybe you could make some curtain tie-backs in a contrasting colour?